This is a walkthrough of my painting process for Calamity Katie, I spent a lot of time giving her face an interesting and monstrous look, mostly through the characterisation of her features and with the use of colour and texture.

Whenever I paint a character, there is usually something I am specifically focusing on, and that focus will determine exactly how I organise my painting. In some paintings I am concentrating on colour for instance, and I will plan my image to give me the specific control I am after over colours. For example the Al Dente character was painted up in greyscale first, and then the two main colours were added on top, each on a separate layer with the blending mode set to colour. This meant that I could establish the values first and then edit the colours independently to get exactly the effect I was after.

As a different example, for the very first image in this series (of the devil) my concern was getting the lighting right, so in this case I built up the 3 separate light sources each on their own layers, enabling me to control them independently of each other.

For Katie though, what I really wanted was to get just the right texture on her skin, so this meant creating a number of layers, so that I could get the exact effect I wanted. Let's see how this evolved.

First of all I drew a sketch in Sketchbook Pro, the purpose of this is to nail down the features and get the characterisation right. I was a after a mixture of appeal and gruesomeness, and humour of course.

Once the sketch is established, I use the Image size dialog in Photoshop to upscale it to high res, in this case 2000 pixels wide by 2600 tall. I then paint on top of this, blocking in the basic local colour of the face which will have its own layer. The mouth and teeth are also on their own layers, above the face, so they won't be affected by what goes on below them.

I keep the original solid green face layer untouched throughout this process, meaning I can always go back and change this local colour. I Alt-click on the New Layer icon at the bottom of the layers palette to bring up the following dialog:

I set the new layer's blending mode to Overlay, tick the box to fill it with the mode's neutral colour (which will be transparent) and also tick the box to use the previous layer as a clipping mask. This gives me a very flexible base to paint on, as you will shortly see.

Using black and white and shades of grey, I simply paint on the Overlay layer using mostly hard brushes, with the occasional dab of airbrush and a little bit of blending with the smudge tool. By using an Overlay layer in this way the shading retains more saturation than if you just painted with black and white, but less saturation than if you use the Dodge and Burn tools on the original. For me it strikes the perfect balance, and it's very easy to tweak the shading without affecting any other elements in the image.

There are alternatives to this method, you can for instance paint with the Dodge and Burn tools on the Overlay layer instead of a brush, with similar results (but never on the original layer, the saturation goes crazy).

Or if you don't want to create a specific layer for shading (and often I don't) then you can paint with a brush over the original colour like this: select the initial colour (in this case the green of the face) and using this same colour set your brush's blending mode to Multiply, lower the opacity to about 20% and paint the shadows. For the highlights set the brush to Screen. This will keep your shading nicely coloured without going dead like it does if you simply paint with black or white, but without over saturating.

At this point I add some stronger shading on a new layer with the airbrush. For the deep shadows I do use black, or a very dark green.

I create a new Overlay layer with the same settings as before, and use the Noise filter to add some texture. I then use the Median filter to make the texture softer and more grainy.

I Alt-click on the New Adjustment Layer in the Layers palette to create a Levels adjustment layer using the underlying face layers as a clipping mask, and boost the contrast.

Next I paint the cracks in Katie's skin. I do this loosely with the Wacom tablet and a hard-edged brush on a new Overlay layer (same settings as before). I initially paint them in black, and once painted I run the Frosted Glass filter on them to create a more natural looking effect. I duplicate the layer, invert the colours and shift the copy slightly down and to the left to create the highlights on the ridges. I then merge the two layers together and lower the opacity to a nice looking level.

I then create another Overlay layer (you can see I'm fond of these), double-click it to bring up the Blending Options dialog, and then go to the Pattern Overlay tab. I select one of the Adobe patterns (from the Rock Patterns library I think) which is an image of lots of little pebbles. I convert the layer style to an actual layer (right-click on the little F icon next to the layer in the layers palette) and merge it down with its parent layer. I then run the Paint Daubs filter on this to make it look like an organic mess of splattery blobs, and lower the opacity to 20%, to create another level of texture on the skin.

I then create a Hue/Saturation adjustment layer, clipped to the same group as the rest, and lower the saturation which is getting a bit too high with all the Overlay effects that are going on – the Overlay blending mode always adds contrast and saturation.

Next I create yet another new layer in the clipping group, this time with the blending mode set to Colour, and using a large soft airbrush I paint in a few areas of colour variation. I some places I make the green a little more yellow, and in others I make it a little more blue. This adds some life and variation to the skin.

Finally I create one more layer, still clipped to those below, and with an airbrush I paint in some much stronger shadow to really define the form of the head.

This essentially completes the painting of the head. It might sound a little fussy having so many layers in use, but it does give a huge amount of control. What I've done here is to keep the shading, colour and textureall separated from one another, and each one can be changed without affecting the others – this is very powerful as it means you can tweak all these elements at any time, for instance reducing the strength of the texture (or even changing it altogether), or changing the colour of the character, or the direction of the light, very quickly and easily. Anyone who works professionally in illustration knows how often things get changed, and this kind of workflow saves an awful lot of time and work.

Of course, on less important elements of the image I proceed with less fuss, for instance the hands are painted with far fewer layers, most of the shading being done right on the original layer with the blending modes assigned to the brush.

I paint the rest of the image, adding eyes, arms and clothing, and finally create a layer at the very top with some rim lighting painted on it to help define the form of the character against the background, and to look pretty.